Once in place, we found a slight gain of 3.0 rwhp and 1.2 lb-ft of torque for a new peak of 341.2 rwhp and 325.3 rwtq. We weren't too surprised of the small gain, because on 2005-2006 GTOs the factory dual exhaust isn't very restrictive at our power level. So, this proves that on a mildly modified LS2 GTO like ours, only a slight gain can be realized with a cat-back on a bolt-on car.
Next up is our upgrade to the last link of the exhaust chain. This means it was time to ditch the factory cast-iron exhaust manifolds and catalytic converter pipes and to switch over to higher-flowing long-tube headers and catalytic converters. Here again, we went with components by Stainless Works to complement our cat-back. Part number 05GTOHCAT ($XXX) comes with 1.75-inch primary tubes and two high-flow catalytic converters by Random Technologies. Installation was typical for a long-tube header in a GTO in that the steering rack had to be disconnected and lowered out of the car while the headers were installed from underneath. It is important to note that once in final position, the headers cleared everything perfectly, including the steering shaft, which has proven to be a common spot for interference with some other brands. Before we cranked the car up, Matt wanted to put a quick tune into the car to help make up for the increased airflow and to prevent piston-killing detonation. Based on his experience, he was able to plug in a tune with his HP Tuners software in just a few minutes. Back on the dyno, our GTO was now pounding out 350.1 rwhp and 336.7 lb-ft of torque, bringing the total gain from the full exhaust upgrade to 11.9 hp and 12.6 lb-ft of torque. Best of all, the car did not get much louder because we still kept our GTO equipped with catalytic converters and the street manners were not degraded one iota.
There is no better way to find out how bolt-ons affect your ride than to take it to the track. So, we slapped on our Nitto Drag Radials and headed over to Atco Raceway for a little test-and-tune fun. With a strong burnout and plenty of mat-the-pedal adrenalin flowing, we were able to lay down a solid 12.286 at 110.70 mph with a 1.650 short time. In total, the bolt-ons allowed us to drop our e.t.'s an incredible 0.334 seconds and we picked up a full mile per hour.
At the end of the day, you want to know how your hard-earned dollars turn into miles of grins and lowered e.t.'s. We hope that our Head Poncho has given you some hard facts and, more importantly, some motivation to get on the dyno and onto the track. In the end, our bolt-on assault was a very rewarding experience for two reasons: we learned what parts make the most power per dollar and, ultimately, were able to dispel many myths that have been running around on the Internet and at the track pits. See you at the strip.